Testing an Ad5-based HIV vaccine in sites around the world

Rachel Tompa

The HVTN 050 trial was a Phase I trial testing a candidate HIV vaccine by Merck for its safety and ability to elicit immune responses. Like the Merck vaccine tested in the Step study, a large Phase II trial of a candidate vaccine that was halted in 2007 due to its failure to protect, the vaccine used in HVTN 050 also used adenovirus 5, or Ad5, as a base, but included parts of only a single HIV gene, gag. The protocol researchers, led by Dr. Scott Hammer, professor of medicine at Columbia University, and including VIDD staff physician Dr. James Kublin, co-director Dr. Steve Self, and member Dr. Ann Duerr, enrolled 360 HIV negative volunteers from 24 sites around the world, including North and South America, the Caribbean, South Africa, and Southeast Asia. Participants were randomly assigned to one of three groups to receive a placebo or higher or lower amounts of the candidate vaccine.

The researchers looked at the safety of the vaccine by assessing reactions such as fever or local inflammation, and looked at the immunogenicity by measuring T cell responses using assays to measure cytokine (IFN-γ) production in response to vaccination. They saw no severe side effects in vaccine recipients, and found that it was immunogenic in most recipients, although volunteers with previous Ad5 infection who received the lower vaccine dose were less likely to respond and had a weaker immune response. This study was the first to test an Ad5-based HIV vaccine in such a wide variety of geographic locations; its findings suggest that an Ad5-based vaccine is well tolerated and may be immunogenic in diverse groups, but more work is needed to understand the interplay between previous Ad5 infection and response to Ad5-based HIV vaccines.